1. Field of the Invention
The present invention relates to a composite crucible to be used for pulling up monocrystalline silicon (single crystal silicon). More specifically, the present invention relates to a composite crucible having superior thermal resistance suitable for pulling up large-size monocrystalline silicon in which a quartz glass as an inner layer and a carbonaceous material as an outer layer are integrated to from a composite structure, and to a preparation method and a regeneration method thereof.
2. Description of the Prior Art
Monocrystalline silicon, namely, single crystal silicon for semiconductor materials are prepared generally by Czochralski method with which monocrystalline silicon is pulled up from a molten polycrystalline silicon. In the method, a quartz glass crucible is used as a material for a vessel for holding the molten polycrystalline silicon therein.
Recently, there has been required a large-size crucible in accordance with requirements of large-sized wafers. As to the large-size crucible for pulling up large size monocrystalline silicon, the period for pulling up monocrystalline silicon becomes longer than that in the conventional ones. In addition, it is used at a higher temperature than the conventional one, thus particularly, thermal resistance strength thereof becomes a problem. Then, there may be considered a counter measure to increase strength by thickening a glass crucible, but the thickness of the glass crucible is limited due to its production procedure. Thus, if a large-size tendency is proceeded more, mechanical strength will become insufficient in the conventional structural ones, which causes deformation of the crucible when used at a high temperature, or which may cause a fracture in being handled.
Generally, the quartz glass crucible is used by fitting to a crucible-form susceptor that is, an outer crucible mounted on a pulling machine. This susceptor is made of carbon. Carbon is used as a thermal resistant material having a high thermal conductivity. However, since there are some partial gaps between the quartz glass crucible and the carbon susceptor to produce loose fitness thereof in the conventional ones, some problems such as swelling, inside falling over or sinking down of the quartz glass crucible wall may be caused. Further, if fitness between the quartz glass crucible and the carbon susceptor being poor, a coefficient of thermal conductivity is lowered and conduction of heat becomes ununiform.
Further, the crucible itself is required to be large in size for pulling up large monocrystalline silicon, which is in turn inevitably accompanied with a large-size carbon susceptor. Thus, in order to make assembly thereof easy, a divided type one has been used. Such divided type susceptor has such a problem that gaps are formed at seams, which causes fracture of the quartz glass crucible, or the like.
Further, since the quartz glass crucible should be fitted to the carbon susceptor every time when used in the conventional method, the operation thereof is troublesome and also contamination may be easily produced at a contacting face of the quartz glass crucible and the carbon susceptor, which may cause conduction of heat ununiform.
On the other hand, there have been proposed several susceptors in which the conventional graphite material is substituted with carbon fiber reinforced carbon (Japanese Patent Application Laid-Open No. Hei 09-263482, etc.) as the improved carbon susceptors. These susceptors have similar problems to the above-mentioned ones, since they are structured as separate bodies from the quartz glass crucibles and they are used after being fitted to the quartz glass crucible.
The present invention has been made to overcome the above-mentioned problems inherent in the conventional quartz glass crucibles, and therefore has an object of the invention to provide a crucible for pulling up monocrystalline silicon with high reliability, and to a preparation method and a regeneration method thereof, in which the crucible has superior mechanical strength, thus it is suitable as a large-size crucible without any deformation when used at a high temperature, and any problem due to insufficient adhesion between the susceptor and the quartz glass crucible is not present, since the conventional carbon susceptor is not necessarily used, thus a high single crystallization yield can be attained.
That is, the present invention relates to a composite crucible for pulling up monocrystalline silicon, comprising an inner layer made of quartz glass and an outer layer made of a carbonaceous material, wherein that the carbonaceous material in the outer layer and the quartz glass in the inner layer are integrally formed.
As preferred embodiments of the present invention, the composite crucible according to the present invention includes (I) one in which the outer layer comprises a laminate of a carbon fiber, (II) one in which the outer layer is made of carbon fibers having an average roughness of a surface, which contacts with a quartz glass in the inner layer, of 0.1-1.0 mm and an average distance between concave and convex parts of 0.2xcx9c5 mm, and (III) one in which the outer layer comprises a laminate of carbon fibers having a gas permeability of 0.5 cm/sec or more.
Also, the present invention relates to a method for preparing a composite crucible for pulling up monocrystalline silicon, which crucible having an inner quartz layer and an outer carbonaceous material layer, the method being characterized by comprising: using a carbon fiber crucible as an outer circumferential part, supplying quartz powders on an inner surface of the carbon crucible while rotating it to be heated and melted; and vitrifying the quartz layer up to the inner surface of the carbon crucible to integrally form the quartz glass layer and the carbon crucible layer, thereby obtaining the composite crucible having a carbon fiber outer layer integrally formed with a quartz glass inner layer.
The preparation method as to said method comprising the steps of: depositing quartz powders on the inner surface of the carbon crucible to be heated and melted; and supplying quartz powders gradually under heating to deposit a melted quartz powder on the quartz layer, thereby obtaining a composite crucible having a transparent glass layer formed in the inner surface thereof.
Further, the preparation method as to said method comprising the steps of: using a carbon fiber crucible having gas permeability as an outer circumferential part; depositing quartz powders on an inner surface of the carbon crucible while rotating it to be heated and fused; reducing the pressure in the crucible through the carbon crucible upon the heating and fusing; sucking and removing the gas contained in the quartz layer; and extruding bubbles contained in the quartz glass layer to form a transparent glass layer on an inner surface of the carbon crucible, thereby obtaining the composite crucible in which the quartz glass layer and the carbon crucible layer are integrally formed.
Further, the present invention relates to a method for regenerating a composite crucible, comprising: heating the crucible from an inner surface side and fusing again a surface of a quartz glass layer, and to a method for regenerating a composite crucible, comprising: removing a quartz glass layer of the composite crucible; supplying fresh quartz powders on an inner surface of the remaining carbon crucible to be heated and fused; and vitrifying the quartz powders to thereby integrally form the quartz glass layer and carbon crucible layer.